Diene rubbers melting point

This situation is identical to the previous one and occurs for example when paraffin wax is mixed into rubber above the melting point of the wax. On cooling, the wax starts to crystallise, some of it forming a bloom on the rubber surface. Such a bloom assists in protecting a diene rubber from ozone attack. 

The two naturally occurring isomers of polyisoprene have quite different physical properties. The chemical structures of cis and trans poly dienes have been discussed in Section 2.5.4. When the chains have a cis configuration crystallization is relatively difficult. The degree of crystallinity in natural rubber is fairly low and the melting-point is just above ambient temperature ( 35°C). The chains in cw-polyisoprene can also coil relatively easily by rotation about single bonds and when the polymer is... 

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